Hardboard, fiberboard, particleboard and similar boards are fabricated from wood fibers or chips and consolidated under heat and pressure. Prefinished hardboard is made by consolidating lignocellulosic fibers under pressure in a press followed by application of one or more primer coats and topcoats. When waferboard, hardboard, or particleboard mat are pressed under heat and pressure in a press to form the various types of board, a press release is needed to prevent the board from sticking to the press plates. Resins, oils, sugars, and the like in the wood chips or fibers migrate to the surface and cause sticking pressplate buildup. Due to the numerous resinous and lignocellulose materials present in the fibers and chips used in hardboards, sticking to the hot mold is quite a common problem even if a mold release agent is used for coating the mold surface. A further problem in hardboard production is often experienced in the end product wherein the hardboard product surface is subsequently finished in a subsequent process. The hardboard surface must further exhibit excellent holdout to decorative paint coating or patterns so as to avoid uneven or excessive absorption of the paint into the fiberboard surface. The pressed board surface is rough and porous giving poor appearance and paint holdout. Current paper overlay coatings applied to board surface to upgrade the board surface are pigmented melamine-thermoset acrylics which tend to stick to the press plates during lamination of the paper to the board. The surface sealers or coatings require a prepress sealer or press plate release to get good plate release and prevent plate buildup.
Prepress sealers are shown in U.S. Pat. Nos. 4,201,802 and 2,635,976, and 4,009,073. Prepaint sealers are shown in U.S. Pat. No. 4,627,999.
It now has been found that a water reducible inpress primer/sealer developed with an internal crosslinker system can be applied as a primer/sealer to resin impregnated, adhesive backed overlay paper and dried (B staged). This primed dried paper can be laminated to a fiberboard composite such as waferboard, particle board, hardboard, or hardboard mat by heat and high pressure in a suitable press, immediately after coating and drying the paper or even up to six months after coating the paper. The coated paper upgrades the rough surface of the waferboard, particle board or hardboard to a primed smooth or textured surface, with good release and no excessive buildup on the press caulplates.
The inpress primer/sealer of this invention has excellent package stability in the can and excellent stability when applied to the overlay paper and flash dried. The coated overlay paper can be stacked in sheets or rolled into a roll with no blocking in the stack or roll. The coated paper can be laminated to the board in a smooth or textured surface with no cracking in deep textures as well as good surface appearance and hiding. The coated paper overlay does not contribute to plate buildup or need extra release or plate treatment. These and other advantages of this invention will become more apparent by referring to the detailed description and illustrative examples.